Polyketides are a diverse class of natural products with an established history of clinical utility (e.g. erythromycin, FK506, Iovastatin). Conventional strain improvement processes are necessary to make therapeutically important polyketides commercially attractive but are time consuming and tedious. The long term goals of this work are to develop generic approaches to polyketide overproduction and then apply these approaches to the generation of novel polyketide antimicrobials. In this proposal, we are targeting the production of novel erythromycin analogs for lead generation and preclinical development of ketolide and motilide therapeutics. Ketolides are a new class of potent antibiotics with activity against erythromycin sensitive organisms. Motilides are motilin receptor agonists being developed for treatment of gastric pariesis, gastric reflux disease and other uses. The specific aims of this proposal are: i.) to use an erythromycin overproducing system developed in Phase I to express several genetically modified erythromycin PKS genes and produce fully mature erythromycin analogs needed for early and late stage testing, and ii.) to adapt the system to one that will efficiently incorporate synthetic diketide-SNAC precursors into the polyketide product and produce erythromycin analogs by precursor-directed biosynthesis. As specific aim iii), we plan to initiate development of a second generation generic overproduction host in the widely used actinomycete host Streptomyces coelicolor. These aims will facilitate the advancement of ketolide and motilide compounds that are in late stage preclinical development, potentially generate new leads for development, and expand the diversity of structures that can be achieved through the genetic manipulation of polyketide synthases in microbiological systems. Furthermore, the establishment of well-defined overproduction hosts will facilitate analyzing the molecular and physiological basis of overproduction. [unreadable] [unreadable]